Central heating pump sizing

[Steel Buttocks]

Open the gate valve fully on the cylinder return. Check all TRVs are fully open or remove a few of the heads. Slow down the pump speed. Check pump valves are fully open. Then try again. If problem persists, i would remove and inspect pump.

 

[Reddwarf4ever]

Open the gate valve fully on the cylinder return. Check all TRVs are fully open or remove a few of the heads. Slow down the pump speed. Check pump valves are fully open. Then try again. If problem persists, i would remove and inspect pump.

It’s a brand new pump & working very well, the main issue is with the boiler controls.....

 

[John.g]

Some very interesting comments in this blog, also explains anti cycling time tables.

Vaillant cycling problem

Vaillant 400-series boilers cycle on and off rapidly when they shouldn't - the stories of their unhappy owners

vaillantcyclingproblem.blogspot.com

 

[Reddwarf4ever]

Hello
read through it all, makes me wonder if Vailant wasn’t the best choice.
as an update, I am now running at 11KW limit, seems to satisfy fast warm up from cold and doesn‘t seem to impact on a boiler restart. Target temperature 62oC and is hot enough to keep the Hot water hot, set for Hot water, 8PM to 830PM and 8AM to 11AM Pump still on PP2, working well, all Rads getting hot. Room stat gets satisfied 2
-3 times a day, allowing the boiler to go off.....so the only thing I need to really resolve is the 3oC hysteresis rather than the 5oC that Vailant say it should be and the over enthusiastic firing amd overshooting.....hoped the heating curve settings could be the solution to this......

 

[John.g]

PP2?? or PP3.

 

[John.g]

A recent post I saw somewhere re a Glowworm "low water pressure" alarm on boiler/pump start up got me thinking about your very first post paragraph re S.53 & S.54. The glowworm alarm (and start inhibit?) is triggered by a pressure sensor which detects the small rise in pressure when the circ pump starts, so obviously if the pump doesn't start or is fouled with sludge etc then this alarm annunciates, the glowworm sensor apparently can get blocked very easily and a temporary fix was to increase the filling pressure and might lead one to falsely believe that this sensor was only used only as a method of detecting sufficient water in the boiler.
Valliant informed you that S.53 is triggered by the 30C flow/return deltaT but I think its triggered by the above (borne out by changing the pump) and S.54 is the deltaT alarm, however if this is correct then the boiler would have to fire up, perhaps on minimum firing?, to enable the high deltaT to develop between the flow/return or else S.54 isn't configured quite correctly. (Or else the boiler just waits and waits to see if S.53 clears).

I also see that you can run the boiler on return temperature by changing d.17, even though you seem to be getting very satisfactory performance now it might be interesting to try this control mode sometime to see its effect on the target (flow) temperature and of course condensing benefit, it is primarily suggested for UFH.
Also may be worth checking that d.18 (pump overrun) is on its default setting 1 ( comfort or continuous running).

Strange, but in all those interesting blog posts I havn't seen it mentioned anywhere that the flow trip is SP+5C.

 

[Reddwarf4ever]

PP2?? or PP3.

Yes PP3.....

A recent post I saw somewhere re a Glowworm "low water pressure" alarm on boiler/pump start up got me thinking about your very first post paragraph re S.53 & S.54. The glowworm alarm (and start inhibit?) is triggered by a pressure sensor which detects the small rise in pressure when the circ pump starts, so obviously if the pump doesn't start or is fouled with sludge etc then this alarm annunciates, the glowworm sensor apparently can get blocked very easily and a temporary fix was to increase the filling pressure and might lead one to falsely believe that this sensor was only used only as a method of detecting sufficient water in the boiler.
Valliant informed you that S.53 is triggered by the 30C flow/return deltaT but I think its triggered by the above (borne out by changing the pump) and S.54 is the deltaT alarm, however if this is correct then the boiler would have to fire up, perhaps on minimum firing?, to enable the high deltaT to develop between the flow/return or else S.54 isn't configured quite correctly. (Or else the boiler just waits and waits to see if S.53 clears).

I also see that you can run the boiler on return temperature by changing d.17, even though you seem to be getting very satisfactory performance now it might be interesting to try this control mode sometime to see its effect on the target (flow) temperature and of course condensing benefit, it is primarily suggested for UFH.
Also may be worth checking that d.18 (pump overrun) is on its default setting 1 ( comfort or continuous running).

Strange, but in all those interesting blog posts I havn't seen it mentioned anywhere that the flow trip is SP+5C.

Hi
fascinating, as Spock would say, I still believe S53 is caused by a 30oC temperature differenc, as I used to run the output at 75-78oC, where it regularly exceeded the 30oC difference......this hasn’t happened once now, as I rarely see a differential that high, typically 20oC Max......D17 is I believe for underfloor heating systems, will have a look, but as you say, it’s running so well now, can’t see how I can improve it, but will give it a go, in the interest of science will check D18....I also haven’t seen any reference to the +5oC cut out, but have an email from Vailant confirming this, so hopefully it’s correct, just need to find out how to fix mine from 3oC to 5oC....

take care.

 

[John.g]

Looks like temperature derived so, I,ve seen that it sometimes displays with deltaTs as low as 22/23c so perhaps looks at the rate of rise of the flow temperature as well, anyway not a problem for you now.

 

[Reddwarf4ever]

Looks like temperature derived so, I,ve seen that it sometimes displays with deltaTs as low as 22/23c so perhaps looks at the rate of rise of the flow temperature as well, anyway not a problem for you now.

Cant believe how silent the boiler and pump are, modulating perfectly @ 62oC DT 11-12oC inlet 52oC house warming up all rads hot......never ever been this good
had problems since 2009 before that my Potterton Netaheat presented no problems, but at 60-65% efficiency wasn’t good.
to save me looking back, was there a calculation for KW being used by the boiler, based on flow / DT maybe ?
Also on a bit of an off topic subject, I have a room stat a Coronado controls 2005 model, it has an ‘ offset ‘ setting of 0.5 or 1.0.....but with a target of 22.5oC it switches on @ 21.5oC and off @ 22.2oC don’t see this makes sense the ’offset’ is set at 0.5.

wonder if it’s faulty or I have misunderstood how it should work.....gets quite cool ( need to keep warm for my Disabled Wife ) before it switches on again....thanks

D18 is set to 0 ( zero ) what would changing it to 1 mean ?

 

[John.g]

The calc for KW is, KW= m3/hr*16.66*60*deltaT/860. = 0.85*16.66*60*12/860, 11.86KW.

This the ref I have to D.18. (1 is the default)